AQA A Level Biology复习笔记5.3.8 Calculating Productivity & Efficiency

• Given the appropriate data, it is possible to calculate the net productivity of producers or consumers and the efficiency of energy transfers within ecosystems

Net productivity of producers

• The net productivity of producers (also known as net primary productivity or NPP) can be calculated using the following equation:

NPP = GPP - R

• Where:
  • GPP = gross primary productivity
  • R = respiratory losses

   

Step 1: Write out the equation and substitute in the known values

NPP = GPP - R

NPP = 10,000 - 5,500

Step 2: Calculate the net primary productivity and give appropriate units

NPP = 4,500 kJ m-2 yr-1

Net productivity of consumers

• The net productivity of consumers can be calculated using the following equation:

N = I - (F + R)

• Where:
  • I = the chemical energy store in ingested food
  • F = the chemical energy lost to the environment in faeces and urine
  • R = the respiratory losses to the environment

   

Step 1: Rearrange the equation to find the total energy loss (F + R)

N = I - (F + R)

(F + R) = I - N

Step 2: Substitute in the known values

(F + R) = I - N

(F + R) = 18,900 - 2,400

Step 3: Calculate the total energy loss and give appropriate units

Total energy loss = 16,500 kJ m-2 yr-1

The efficiency of energy transfers within ecosystems

• In some cases, the efficiency of energy transfer refers to the percentage of energy that is transferred from the sun to producers
  • This can be calculated using the following equation:

   

% Efficiency = (gross primary productivity ÷ light energy falling on the producer) × 100

• In other cases, the efficiency of energy transfer refers to the percentage of energy that is transferred from one trophic level to a higher trophic level (e.g. from producers to primary consumers or from primary consumers to secondary consumers)
  • This can be calculated using the following equation:

   

% Efficiency = (chemical energy in consumer ÷ chemical energy in ingested food) × 100

• If it is a producer that is being ingested (e.g. by a primary consumer), the chemical energy in the ingested food is the same as the net primary productivity of the producer and the chemical energy in the consumer is the same as the net productivity of the consumer, so that:

% Efficiency = (net productivity of consumer ÷ net primary productivity ) × 100

• If it is a consumer being ingested (e.g. a primary consumer being ingested by a secondary consumer), the chemical energy in the ingested food is the same as the net productivity of the consumer being ingested and the chemical energy in the consumer is the same as the net productivity of the consumer (that is doing the ingesting), so that:

% Efficiency = (net productivity of secondary consumer ÷ net productivity of primary consumer) × 100

Step 1: Write out the equation and substitute in the known values

% Efficiency = (gross primary productivity ÷ light energy falling on the producer) × 100

% Efficiency = (4.25 × 103 ÷ 6 × 105) × 100

Step 2: Calculate the efficiency

% Efficiency = (0.0071) × 100

% Efficiency = 0.71 %

Step 1: Write out the equation for % efficiency and substitute in the known values

% Efficiency = (chemical energy in consumer ÷ chemical energy in ingested food) × 100

or

% Efficiency = (net productivity of consumer ÷ net primary productivity ) × 100

% Efficiency = (10,000 ÷ 112,500) × 100

Step 2: Calculate the efficiency

% Efficiency = (0.089) × 100

% Efficiency = 8.9%

Step 1: Calculate the net production of the toads

N = I - (F + R)

N = 10,000 - (2,000 + 7,000)

N = 10,000 - 9,000

N = 1,000 kJ m-2 yr-1

Step 2: Write out the equation for % efficiency and substitute in the known values

% Efficiency = (chemical energy in consumer ÷ chemical energy in ingested food) × 100

or

% Efficiency = (net productivity of secondary consumer ÷ net productivity of primary consumer) × 100

% Efficiency = (1,000 ÷ 10,000) × 100

Step 3: Calculate the efficiency

% Efficiency = (0.1) × 100

% Efficiency = 10%